Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer sheets that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass typically refers to a transparent laminate comprising a poly(vinyl butyral) sheet disposed between two panes of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening. Additives to the sheet formulation generally include at least one adhesion control agent (hereinafter, “ACA”) to modify adhesion of the sheet to the glass so that a suitable level of adhesion can be maintained to prevent spalling of the glass while still providing adequate energy absorption if an impact occurs.
Safety glass can be formed by a process in which two layers of glass and a plastic interlayer, such as poly(vinyl butyral), are assembled into a pre-press, tacked into a pre-laminate, and finished into an optically clear laminate. The assembly phase can involve laying down a piece of glass, overlaying a poly(vinyl butyral) sheet on that glass, laying down a second piece of glass on the poly(vinyl butyral) sheet, and then trimming the excess poly(vinyl butyral) to the edges of the glass layers.
The plastic interlayer can be produced by mixing poly(vinyl butyral) polymer with one or more plasticizers, and optionally with one or more other ingredients, and melt processing the mix into sheeting, which typically is collected and rolled for storage and transportation.
The process of fabricating poly(vinyl butyral) resin can entail the use of acids to catalyze the formation of a vinyl acetal from vinyl alcohol and aldehyde precursors. After formation of the acetal, the acids can be neutralized using an appropriate base. This process will typically leave residual acetate trapped within the poly(vinyl butyral) resin, which can impact both stabilization and adhesion qualities. The residual concentration of the acetate, however, can be a limiting factor when certain adhesion and other characteristics are desired in the finished poly(vinyl butyral).
Accordingly, further improved compositions and methods are needed to enhance the characteristics of polymer and poly(vinyl butyral) sheets, and specifically poly(vinyl butyral) sheets, without adversely affecting the resulting polymer sheet.